If you see the Ent rate for your dates, call in-house reservations and book it ASAP, because those dates tend to sell out quickly.
If you don't see it, book for the 15% off DISboards rate; then if they add your dates back in again closer to your stay (which they often do, last minute, if their bookings need a boost) then call ASAP and they will adjust your rate to the better rate.